You are likely thinking of a protist, specifically a ciliate. Ciliates are a type of single-celled organism that have a flexible outer layer called a pellicle.

Here's how the pellicle's flexibility allows them to do these things:

* Change shape: The pellicle allows ciliates to change shape, which is essential for movement and for navigating through their environment.

* Move: The pellicle helps maintain the shape of the ciliate while its cilia (tiny hair-like structures) beat rhythmically, propelling it through the water.

* Avoid predators: The pellicle provides a degree of protection, allowing the ciliate to contract and squeeze through tight spaces, potentially escaping predators.

Let me know if you'd like to know more about the pellicle or ciliates!